Electric circuit breaker or the magnetic blowout type

ABSTRACT

An electric circuit breaker of the magnetic blowout type comprises an arc chute having spaced-apart arc runners positioned between the pole pieces of the magnetic blowout means. Each of the arc runners comprises elongated structure of ferromagnetic material and a coating of arc-plasma sprayed tungsten bonded to a surface of said ferromagnetic structure for defining at the exposed side of the coating an arc-running surface along which one arc terminal moves.

United States Patent [11] 3,801,760 Korte Apr. 2, 1974 [5 1 ELECTRIC CIRCUIT BREAKER OR THE MAGNETIC BLOWOUT TYPE Primary Examiner-Robert S. Macon Attorney, Agent, or FirmWilliam Freedman; J.

[75] Inventor: llillchartl M. Korte, West Chester, Wesley Haubner [73] Assignee: General Electric Company,

Philadelphia, Pa. 5 7] ABSTRACT Filed! g- 1972' An electric circuit breaker of the magnetic blowout L J type comprises an arc chute having spaced-apart are [211 App No 283227 runners positioned between the pole pieces of the magnetic blowout means. Each of the arc runners [52] U.S. Cl. 200/144 C, 200/147 R comprises elongated structure of ferromagnetic mate- [51] Int. Cl. H01]: 33/10 rial and a coating of arc-plasma sprayed tungsten [58] Field of Search ZOO/ C, 144 147 R bonded to a surface of said ferromagnetic structure for defining at the exposed side of the coating an arc- [56] References Cited running surface along which one are terminal moves.

UNITED STATES PATENTS 3,588,405 6/1971 Bailey et al. zoo/144 C 14 Chums 10 Draw F'gures T UN 65 TEN C 0/4 77/V6 77 W/IV/l co /=0? 67554 24 FLA mve 78 ELECTRIC CIRCUIT BREAKER OR THE MAGNETIC BLOWOUT TYPE BACKGROUND This invention relates to an electric circuit breaker of l the type that relies upon magnetic blowout means for In the type of arc chute that I am concerned with, sidewalls of insulating material extend between the arc runners, and plates of insulating material extend transversely of the sidewalls with edges for engaging the arc as it movesinto the chute. Typically, in such an arc chute, during high current interruptions, a large volume of hot ionized gases is developed by the high temperature arc reacting with the components of the chute; and these gases are expelled through the exhaust end of the arc chute. For collecting and cooling these exhaust gases and subsequently venting them via predetermined dielectrically safe paths, it is customary to provide around the arc chute a housing of insulating material, referred to hereinafter as a box barrier, that contains a chamber in which the exhaust gases are received. This chamber typically has outlets that are located in positions near the exhaust end of the arc chute through which the gases can be safely vented. Examples of this type construction appear in US. Pat. Nos. 2,293,452-Boehne; 2,293,513-Linde; and 2,457,002- Spiro.

To insure that the vented gases will be sufficiently cool before leaving the box barrier chamber, it is customary to provide coolers in the outlets from this chamber and, in some cases, to provide another cooler in the exhaust between the arc chute and the box barrier chamber. Examples of these coolers appear in the aforesaid Boehne and Linde patents and also in my joint US. Pat. No. 3,555,224. Unfortunately, these coolers can be quite expensive; and, moreover, despite their presence, it is usually necessary to provide a relatively large clearance space between the cooler in the box barrier vent and nearby grounded structure in order to maintain sufficient dielectric strength through the gases being vented.

SUMMARY An object of my invention is to eliminate the need for any such coolers, either in the arc chute exhaust passage or in any vent from the box barrier chamber.

Another object is to eliminate the need for any substantial vent passages from the box barrier chamber, especially any such vent passages located adjacent the arc chute exhaust.

Another object is to greatly reduce the volume of metallic vapors that the arc generates from the metal are runners as its terminals move therealong during an interrupting operation.

. Another object is to attain the immediatelypreceding object without significantly detracting from the magnetic field from the magnetic blowout means used for driving the are into the chute.

In carrying out my invention in one form, I provide an arc chute, having spaced-apart arc runners and magnetic blowout means comprising spaced-apart pole pieces between which said runners are positioned. Each of the arc runners comprises elongated structure of ferromagnetic material and a coating of thermallysprayed refractory metal bonded to a surface of said ferromagnetic structure for defining at the exposed side of the coating an arc-running surface along which an arc terminal moves.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view partly in section showing an electric circuit breaker embodying one form of the invention. One sidewall of the arc chute has been removed to show the interior of the arc chute.

FIG. 2 is a cross sectional view taken along the line 22 of FIG. 1, assuming the arc chute is assembled.

FIG. 2a is an enlarged sectional view along the line 2a2a of FIG. 1. I

FIG. 3 is a sectional view taken along the line 33 of FIG. 1.

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 1.

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 1.

FIG. 6 is an enlarged view of a portion of FIG. 1.

FIG. 7 is a somewhat schematic, enlarged sectional view of the microstructure of the coating applied to the arc runners.

FIG. 8 is a schematic view illustrating a typical instantaneous configuration of the arc in one of its terminal regions adjacent a runner.

FIG. 9 is a schematic view illustrating another typical instantaneous configuration of the arc in one of its terminal regions adjacent a runner.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT ARC CHUTE STRUCTURE GENERALLY Referring now to FIG. 1 of the drawing, the circuit breaker shown therein comprises a pair of terminal bushings l and 2, both of which are fixed in position relative to the supporting frame (not shown) of the circuit breaker. The bushing 2 comprises a downwardly extending conductive stud 3 at the lower end of which a movable conductive switch blade 4 is mounted by means of a fixed pivot 5. At its outer end, the blade 4 carries suitable circuit-controlling contacts such as a main current-carrying contact 6 and an arcing contact 7.

Bushing 1 comprises a conductive stud 1a to which a downwardly extending conductive member 8 is electrically connected. Attached to this conductive member 8 is a curved contact-retaining member 9 which coacts with the member 8 to form a holding pocket for re- 7 ceiving the anchored ends of main stationary currentcarrying contact fingers 10. These fingers are pivotally mounted on a curved portion 12 of the conducting member 8 and are biased for limited rotative wiping movement in a closing direction by means of suitable compression springs 9a. These compression springs provide for high pressure circuit-closing engagement between the stationary current-carrying contact 10 and the movable main current-carrying contact 6.

The movable arcing contact 7 cooperates with stationary arcing contact 13, which is mechanically and electrically connected to the conducting member 8 by suitable conductive means 14. The material of which the arcing contacts 7 and 13 are made is capable of withstanding arcing and is also of relatively high resistivity in comparison to the material of the currentcarrying contacts and 6. Accordingly, when the switch blade 4 is in its closed position as shown in FIG. 1, most of the circuit current flows through the currentcarrying contacts. It is only when the switch blade 4 is driven counterclockwise to open the breaker that the arcing contacts carry appreciable current. During contact-opening action, the current-carrying contacts part first, thereby diverting current through the arcing contacts which are still in engagement owing to their extensive wipe. Thereafter, the arcing contacts part and draw a circuit-interrupting arc therebetween which is driven into an arc chute l5 and there lengthened, cooled and extinguished.

For driving the switch blade 4 counterclockwise to effect circuit interruption, a reciprocable operating rod 16 pivotally joined to the switch blade at point 17 is provided. When this operating rod is driven upwardly,

it acts to move the switch blade counterclockwise to effect a circuit-interrupting operation. In dotted line form in FIG. 1, blade 4 is shown passing through an intermediate position 58 during an opening stroke. An arc, shown in dotted line form at 59, has been established, and its upper terminal has begun moving into the chute along runner 24 (soon to be described). The circuit can be reestablished after an opening operation by driving the operating rod downwardly to return the switch blade 4 in a clockwise direction to the closed position illustrated in FIG. 1. The operating rod 16, which is made of insulating material, is actuated by means of a suitable conventional operating mechanism (not shown).

The arc chute comprises a pair of side walls 18 and 19 constructed of an arc-resistant and trackingresistant insulating material soon to be described in greater detail. As shown in FIG. 3, these side walls are clamped together in spaced-apart relationship by means of transverse bolts 20a extending between opposite sidewalls at the top and bottom of the chute. Each side wall is provided with plurality of fins 22 projecting toward the other side wall and arranged to interleave with the corresponding projecting fins on the other side wall, thereby forming a sinuous or zigzag passage as viewed either from the entrance end or from the exhaust end of the chute. The view from the latter end is illustrated in FIG. 3.

In the illustrated form of the invention, each side wall comprises a plurality of short ribs 1 l which are respectively disposed between the fins 22 of the associated sidewall in spaced relation to the fins. These ribs 1 1 extend parallel to the fins 22 and are disposed in alignment with the fins on the opposite sidewall.

Referring to FIG. 2, the forward edges of the interleaving fins 22 taper toward the arc-initiation region at the right hand end of the chute. The tapering edges of each adjoining pair of fins 22 intersect as viewed in FIG. 2 to form an entrance angle such as a at the entrance to the zig-zag passage between the fins. The vertexes of these entrance angles all lie on a curvilinear line 23 (FIG. 1) which constitutes their locus. The region of the arc chute immediately adjacent this line 23 is referred to hereinafter as the vertex region of the arc chute.

For facilitating movement of the are into the arc chute, a pair of conductive arc runners 24 and 25 are provided along opposite edges of the chute. The side walls 18 and 19 extend between these runners 24 and 25. As shown in FIG. 1, runners 24 and 25 extend generally transverse to the axis of the are and in divergent relationship with respect to each other from the arcinitiation region adjacent the separable contacts. During an opening operation, shortly after the contacts part to initiate the arc, its upper terminal transfers to upper runner 24, as depicted at 59. Later in the opening operation, the lower arc terminal transfers to lower runner 25; and the arc terminals move along runners 24 and 25 into the chute.

The region of the arc chute where the diverging arc runners 24 and 25 are spaced apart by the least distance we refer to as the throat region of the arc chute. This throat region is designated in FIG. 1. In the throat region 50, there are two separate throat pieces 60, each constituting a sidewall with short fins, or ribs 62, integrally formed therewith. These throat pieces 60 are best shown in FIG. 5, where it can be seen that there is no interleaving of their ribs 62.

Projecting from and electrically connected to the upper runner 24 are two probes 51 having tips of a refractory conductive material. The probes are located immediately adjacent but slightly spaced from the movable switchblade 4. The purpose of these probes is to accelerate transfer of the upper arc terminal to the upper arc runner 24.

The are chute further comprises a first group of blowout electromagnets 26, 27 and 28 mounted adjacent the upper arc runner 24 and a second groupof blowout electromagnets 29, 30 and 31 mounted adjacent the lower arc runner 25. Each of these blow-out magnets comprises a generally U-shaped structure that comprises a pair of pole pieces 32 and 33 constituting the legs of the U and an interconnecting core member 34 between the legs of the U. Each blowout magnet straddles the chute with its pole pieces mounted at the outer sides of sidewalls 24 and 25 and its core member extending between the sidewalls on the right hand side of the arc runners, as seen in FIG. 1. Mounted around the cores of the blow-out magnets are blow-out coils 26a, 27a, 28a, 29a, 30a and 31a. Each blow-out coil is round and its inside diameter is such that it snugly surrounds an insulating sleeve (not shown) on the round cross-section core on which it is mounted. The blowout coils in the upper group are connected in series relationship with each other, and those of the lower group are also connected in series with each other.

With respect to the electrical connection of the upper blow-out coils note that the upper arc runner 24 is divided into a plurality of segments separated by insulating members 52 and 53. Blow-out coil 27a electrically bridges insulating member 52, and blowout coil 28a electrically bridges insulating member 53. The first of the upper blowout coils 26a is electrically connected between the stud 1a and the first segment of the arc runner. In a similar manner, the lower blow-out coils 30a and 31a electrically bridge insulating members 54 and 55 between segments of the lower runner. The first of the lower blow-out coils 29a is electrically connected between the first segment of the lower runner and the conductive stud 3 by means of an electric conductor 57.

When the contacts of the circuit breaker are closed, the blow-out coils are not in the power circuit and are consequently deenergized. When the contacts are separated to form an arc, movement of the are along the arc runners 24 and 25 into the chute connects these blow out coils in series with the arc in a known manner. An important purpose of the blow-out magnets is to propel the arc and accelerate its movement along the runners 24, 25 into the interior of the arc chute. When a particular blow-out coil is energized, the magnetic field pro duced between its pole pieces extends transversely of the arc column. This magnetic field reacts with the magnetic field surrounding the arc in a known manner to produce a resultant force that drives the are at high speed toward the interior of the chute.

In one form of the invention, the pole pieces 32 and 33 of the blow-out magnets are constructed in the manner disclosed and claimed in my joint U.S. Pat. No. 3,591,744, assigned to the assignee of the present invention, and reference may be had thereto for a more complete description of the pole pieces and the manner in which they control the magnetic field that drives the are into the chute.

As the arc terminals move along the runners into the chute, the column of the arc moves freely into the chute until it encounters the intersecting forward edges of the interleaving fins 22 at the vertex region 23. Thereafter, further penetration of the arc chute causes the arc column to assume a zig-zag form as it bends around the overlapping edges of the fins 22, as shown in FIG. 2a. This elongation of the arc and the cooling that results from the intimate engagement of the arc and fins are important factors contributing to successful interruption.

BOX BARRIER 65 FOR COLLECTING ARCING PRODUCTS As the arc moves into the chute, it evolves gaseous arcing products, some through vaporization of arcrunner material by the arc terminals thereon and some through vaporization by the arc of insulating material from the sidewalls 18 and 19 and the fins 11 and 22. These gaseous arcing products are expelled from the arc chute through an exhaust passage 64 at its rear end.

For receiving these gaseous arcing products that are expelled through exhaust passage 64, a-housing 65of insulating material is provided about the arc chute. This housing 65 is referred to herein as a box barrier. In a polyphase circuit breaker, such a box barrier is provided about'the arc chute in each phase, which is a conventional practice. Box barrier 65 has top and bottom walls 66 and 67, vertically-extending sidewalls 68 and 69, and vertically-extending rear andfront walls 70 and 72. Rear wall70 is spacedfrom the rear end of the arc chute to form a gasreceiving chamber 74 between this rear wall 70rand the rear of the arc chute, the chamber being bounded on its sides by portions of the sidewalls 68-and 69.

In prior circuit breakers ofthis general type, the box barrier 65 is provided with vents atthe top and bottom of the chamber 74, as is shown for example in the aforesaidzBoehne U.S. Pat. No. 2,293,452 and Linde U.S. Pat. No. 2,293,513. In these prior circuit breakers, the arcing products are vented through such vents, and

suitable coolers are provided in the vents to cool the arcing products as they pass therethrough. To assure that these vented gases do not produce a dielectrically weak path, susceptible to arc-over, to surrounding grounded structure (not shown), it has been customary to provide a large clearance space between the vents and the grounded structure. To further cool the arcing products before they are vented, it has also been customary to provide a cooler in the exhaust passage 64 between the arc chute and the chamber 74, as is shown, for example, in the aforesaid Linde U.S. Pat. No. 2,293,513 and in my aforesaid joint U.S. Pat. No. 3,555,224.

These coolers are quite expensive, and an object of my invention is to eliminate the need for such coolers and also to eliminate the need for the clearance space heretofore provided between the region where the boxbarrier vents were located and surrounding grounded structure.

ARC RUNNERS I am able to attain the above object by forming the arc runners 24 and 25 of a combination of materials that greatly reduces the quantity of metallic vapors generated by arcing and is responsible for exceptionally high speed are motion thereon. More specifically, I form each of the arc runners of a steel, or ferromagnetic, base and a thin coating 77 of thermally-sprayed refractory metal, preferably tungsten, on its arcexposed face. Although pure tungsten is the preferred material for coating 77, my invention in its broader aspects comprehends the use of other refractory metals such as molybdenum or a combination of a refractory metal and a high-conductivity metal such as copper. Specific examples of such refractory coating materials are disclosed in U.S. Pat. No. 3,588,405-Bailey et al., assigned to the assignee of the present invention.

Generally speaking, my arc runners are made by providing bare steel parts of the shape of the parts of the illustrated arc runners and then plasma-arc spraying tungsten onto these parts. However, before any such spraying takes place, I plate the bare steel arc runner part with a corrosion-protective material such as copper. Then I roughen the surface that is to be closest to the arc terminal, preferably by gritblasting. This grit blasting removes all or almost all of the copper from the roughened surface but leaves the other surfaces of the runner with their copper coating intact, as shown at 79 in FIG. 4. Then the roughened surface is thermally sprayed with tungsten by plasma-arc spraying in the general manner described in U.S. Pat. No. 3,5 88,433-Bailey et al., assigned to the assignee of the present invention. As pointed out in that patent, a conventional plasma-arc spray gun is utilized. Inside this gun, an electric arc is formed and a suitable gas is passed through the region of the arc to form a stream of extremely hot arc-plasma. Tungsten, preferably in powdered form, is fed into the arc-plasma stream, where it is melted and converted into atomized droplets of molten tungsten, which are ejected through a suitable nozzle at high velocity in the plasma stream. The plasma stream containing the molten droplets is projected onto the arc runner, and upon striking its surface, the molten particles freeze and flatten into an adherent coating 77. FIG. 7 is an enlarged sectional view, somewhat schematic, of the microstructure of the coatabout mils in the arc-initiation region and in the regions just ahead of the insulating spacers 52-55, but in all other regions the thickness is only about 5 mils.

Referring next to the cross-sectional view of FIG. 4, it will be seen that the arc runner is sandwiched between the sidewalls 18 and 19 in such a manner that only its tungsten-covered face is exposed to the arc. The edges of the arc runner and its back surface are shielded from the are by reason of the seal that is formed between each sidewall and the contacting edge of the runner. Thus, substantially none of the copper plating 79 is exposed to or vaporized by the arc terminal. The main purpose of the copper plating is to protect the edges and back surfaces from rusting despite heating of the runner by the arc thereon.

COMPARISON WITH PRIOR ART RUNNERS The advantages of my above-described steel-tungsten combination as compared to previously-used are runner materials will now be discussed.

In the aforementioned US. Pat. No. 3,588,405- Bailey et al the use of thermally-sprayed tungsten is proposed for the exposed face of the arc runners. But the base material on which the tungsten is sprayed in the Bailey et a] patent is brass. For various reasons which will be referred to hereinafter, a much greater volume of metallic vapors is evolved from such runners than from my tungsten-coated steel runners, assuming an arc of the same current content. When the runners of the Bailey et al patent have been used, it has been necessary to construct the box barrier with the prior art vents and coolers hereinabove described.

Although steel has heretofore been used as an arcrunner material, it has generally been considered a rather undesirable one for high current circuit breakers with magnetic blowout means, such as my high current circuit breaker with its magnetic blowout means 26-32. This was considered to be the case because (as shown in FIGS. 1 and 4) the runners almost completely bridge the gap between the: pole pieces 32, 33 at opposite sides of the arc chute; and if of steel, they would appear to form a flux-shunting magnetic path between the pole pieces for flux from the blowout coils. Such flux shunting was thought to harmfully reduce the flux from the blowout coils in the region where needed, i.e., adjacent thearc runner. I have confirmed this flux-shunting effect by measuring the flux adjacent the runners with the blowout coils energized, but with no arc present. These measurements have shown that the magnetic field from the blowout coils in the region of and external to the arc runners is reduced by about 66 percent if the arc runners are of steel instead of a non-magnetic material such as brass.

l have not been able to measure the flux present in this region when a high-temperature arc is present, but the evidence now available indicates, surprisingly enough, that when such an arc is present, the presence between the pole pieces of a steel runner, as compared to a brass one, causes little or no reduction in the blowout coils magnetic field external to the runner. The explanation for this, I believe, is that the current through the runner itself behind the are terminal (as shown in FIG. 8) or through the portion of the arc adjacent the runner (when the arc has the configuration shown in FIG. 9) will set up fields within the steel runner to saturate the runner, thus preventing diversion of the blowout coils external field through the runner. Referring to FIG. 8, which shows a typical instantaneous configuration of the are 59 in its terminal region as it moves along runner 24, current passing through the arc enters the runner 24 at the arc terminal and flows via path to an exit point 91. The magnetic field (indicated at 92) around the path 90 produces the above-mentioned saturating effect on the material of the runner. Referring to FIG. 9, which shows another typical instantaneous configuration of arc 59 in its terminal region, the current through the arc portion 94 adjacent and paralleling the runner 24 sets up a magnetic field 92 which likewise saturates the material of the runner in the region 95 alongside arc portion 94.

Bare steel is not a satisfactory arc-runner material for an air circuit breaker, such as shown, because bare steel after being exposed to an arc has a strong tendency to rust severely. The heating and surfacecleaning effect of the arc renders the steel vulnerable to oxidation from the surrounding air, particularly if there is any appreciable humidity. In view of this strong tendency to rust, steel runners, where used, have typically been provided with a protective coating of some easily-platable material such as zinc or copper. Such plated steel runners have generally been avoided for high current circuit breakers with magnetic blow-out means, primarily because they were thought to be inferior to brass or copper runners. This viewpoint was based upon the above-described previously-held belief that the steel runner would divert needed flux from the blowout coils away from regions where it is required and upon the fact that a high-current arc can rapidly evaporate the plating and leave the underlying steel exposed to rusting.

As pointed out hereinabove, my arc runners comprise a steel substrate and a coating of refractory material, tungsten, on their exposed surfaces. The extremely high boiling point of tungsten reduces the volume of vapors evolved by the arc. But more than this, the steel substrate beneath the tungsten coating causes the arc to move much faster than the arc does where a nonmagnetic substrate such as brass is present, thus reducing the exposure of the tungsten to the arc and keeping its temperature lower. This faster movement of the arc terminal on the tungsten-coated steel runners is evidenced by the appearance of the arc runner after an interrupting operation. Closely spaced arc-track spots can be seen on the runner along the paths taken by the arc terminal, indicating that the arc terminal has moved by the so-called walking mode, i.e., in discrete steps instead of continuously. This walking mode is described in more detail in a paper by Winsor et al entitled Properties of a D-C Arc in a Magnetic Field, AIEE Transactions, Vol. 75, Part I, 1956, pages 143-148. Similar spots are present after interruption on a brass runner coated with tungsten, as in the aforesaid Bailey et al patqn.t .2.i8 5; ut i h. ttgstsqlflbsttate ma enta? spots are much smaller and more numerous, thus indicating much higher arc-running speeds. The magnetic character of the substrate is considered to play an important role in producing these higher arc-running speeds. The thinness of the coating 77 also contributes to the higher arc-running speeds, permitting closer proximity of the magnetic substrate and the arc portion 94 when the arc has the configuration depicted in FIG. 9, thus increasing the forces of magnetic attraction between arc portion 94 and the adjacent portion of the runner.

Using arc-runners constructed as abovedescribed of steel and a thermally-sprayed tungsten coating, I have been able to reduce the volume of the arcing products passing through exhaust passage 64 into the box barrier chamber 74 to such a great extent that the previouslyused vents from chamber 74 can be completely eliminated. Even when interrupting the highest currents for which the circuit breaker is rated (e.g., 27,000 amperes in one embodiment), the vents were found to be unnecessary. Moreover, I am able to accomplish this result without the need for any cooler in the exhaust passage 64 between the arc chute and box barrier chamber 74. The box barrier 65 is completely sealed except for a small opening 80 provided around the terminal bushingsl and 2 to facilitate assembly of the box barrier. This opening 80 could also be sealed, if desired, and no substantial adverse effect would be had on interruption. Sealing of opening 80 is, however, unnecessary because opening 80 is so far away from the chamber 74 receiving the exhaust gases from the arc chute that any gases flowing through opening 80 contain an insignificant quantity of still-ionized arcing products and are therefore dielectrically strong.

A barrier 82 of insulating material, front end wall 72, and other insulating material barriers (not shown) in the arc-initiation region of the circuit breaker are provided to restrict the flow of arcing products from the arc-initiation upwardly through the opening 80 or in a direction to the right in FIG. I. The flow of arcing products from the arc-initiation region downwardly and to the right in FIG. 1 is restricted by the front end wall 72 and the bottom wall 67 of the box barrier, both of which are substantially imperforate.

As pointed out hereinabove, it has heretofore been necessary to provide a clearance space between adjacent grounded structure and the previously-used vents that were provided at the top and bottom of box barrier chamber 74 in order to assure against an arc-over .through the vented gases. I am able to dispense with such clearance space, as is evidenced by the presence of grounded structure 85 at the top of the box barrier 65 in the region where one of the prior vents was located. Eliminating the need for such clearance space enables me to attain a more compact overall construction. It is to be understood that all the internal surfaces of the wall portions of chamber 74 are of insulating material and are thus isolated from ground.

Another advantage of my steel-tungsten arc-runner material combination is that it extends the life of the arc-chute. This life is determined primarily by the amount of metal condensate condensing on the insulating surfaces of the arc chute. By materially reducing the quantity of metallic vapors evolved from the arc runner by arcing, I can materially reduce the amount of metal condensate condensing on the insulating surfaces, thereby prolonging the arc chutes life.

Still another advantage derived from my steeltungsten arc-runner combination is that because the arc terminal moves very rapidly thereon, I can reduce the thickness of the tungsten coating as compared to that applied to brass, as in the aforesaid Bailey et al patent.

Still another advantage is that steel-base arc-runners are less costly and easier to fabricate than those made of brass or the like. In this respect, other parts such as the probes 51 and terminals 96 can be joined to the runners by an inexpensive fastening process, such as welding, instead of the brazing used with non-ferrous runners. In a preferred form of my invention, shown in detail in FIG. 6, probe 51 comprises a steel body 88 with an integral steel head 86 thereon. The steel body extends through a closely fitting hole in the arc runner and the head 86 is fastened by spot welding to the back of the runner. The tip 87 of the probe is made of an arcresistant material such as tungsten-copper suitably joined to body 88 before incorporation in the runner. During the plasma-arc spraying step referred to hereinabove, the probe 51 as well as the arc-runner 24 is coated with tungsten.

ADDITIONAL DISCUSSION Although high-speed arc motion on the runners is desirable and is facilitated by the steel-tungsten combination of my arc runners, it is imporatnt that the are not be moved through the arc chute so fast that it reignites across the rear end of the chute. Several features are present in my arc chute to block such excessively fast arc motion under the influence of the tungsten-steel runners. One such feature is the interleaving fins 11 that extend transversely of the arc, engaging it, and impeding its motion toward the exhaust end of the chute. Another such feature is that the insulating material of the arc chute does evolve some gases that build up a back pressure tending to oppose arc motion through the arc chute. In this respect, at least the portion of the arc chute to the left of vertical line 78 (FIG. 1) has its exposed walls .of a material capable of evolving gases when exposed to the arc, e.g., the phospho-asbestos material of U.S. Pat. No. 2,366,485-Brink et al. and U.S. Pat. No. 2,704,38l-Nelson. The remainder of the arc chute can be of the same material, either heat treated to reduce gas evolution or coated with a fused silica coating such as described and claimed in copending application Ser. No. 162,43l-Frind et al.

To facilitate low current interruptions, I employ a puffer tube such as shown (at 40-45) in U.S. Pat. Nos. 2,280,616 and 2,347,984-Baskerville (which patents are incorporated by reference herein) to provide a blast of gas for forcing the arc on the runners into the chute. At low currents, the above-described magnetic saturating effect of the arc runners is not available to prevent flux from the magnetic blow-out means fiom being diverted away from the runners; but at low currents, the magnetic force on the are from the blow-out means is not very significant anyway. The air blast from the puffer provides the principal force for moving the are into the chute. Additionally, some arc-motivating force is provided by the magnetic effect of the U- shaped path of the current passing through each runner and the adjacent position of the arc, as depicted in FIGS. 8 and 9, and this force remains despite the above-described flux diversion. So altogether the presence of the steel-base arc runners does not detract from the low-current interrupting abilities of the circuit breaker.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scopeof my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker comprising an arc chute into which an arc is adapted to be driven for the purpose of extinguishing the arc, said arc chute having an exhaust end and comprising:

a. a pair of spaced sidewalls of insulating material extending along the length of said arc as the arc moves within said chute,

b. a pair of conductive arc runners spaced apart within said chute for defining paths along which the terminals of said arc travel as the arc moves within the arc chute, I

c. magnetic blow-out means for developing in the region between said runners a magnetic field that extends transversely of said paths for providing a force on said arc that moves said arc terminals along said runners towards said exhaust end, said magnetic blowout means comprising pole pieces located on the outer sides of said sidewalls in positions where at least one of said are runners is located between said pole pieces, and coil means coupled to said pole pieces for developing said magnetic field when energized,

d. each of said arc runners comprising elongated structure of ferromagnetic material and a coating of thermally-sprayed refractory metal bonded to a surface of said ferromagnetic structure for defining at the exposed side of the coating an arc-running surface along which one of said arc terminals moves,

e. said thermally-sprayed coating comprising superimposed flattened and interlocking particles of refractory metal bonded together.

2. The circuit breaker of claim 1 in which said refractory metal is arc-plasma sprayed tungsten.

3. The circuit breaker of claim 1 in which said thermally-sprayed refractory metal coating covers substantially the entire surface of each of said arc runners that is exposed to an arc terminal.

4. The circuit breaker of claim in which said thermally-sprayed refractory metal coating covers substantially the entire surface of each of said are runners that is exposed to an arc terminal.

5. A circuit breaker as defined in claim 1 and further comprising:

a. an arc-initiation region in which said are is initiated,

b. a probe projecting from one of said runners towards said arc-initiation region for accelerating arc transfer to said one runner,

c. said probe having a body portion of ferromagnetic material joined to said one runner,

d. and a coating of thermally-sprayed refractory metal covering the region of said body portion that is exposed to said arc.

6. The circuit breaker of claim 1 in which: each of said are runners has inactive surfaces that are free from said thermally-sprayed refractory metal coating, said inactive surfaces being constituted by a non-ferrous rust-resistant coating on said ferromagnetic material,

and sealing means is provided between said refractory meta] coating and said inactive surfaces for preventing said arc terminals from contacting said inactive surfaces.

7. An electric circuit breaker as defined in claim 1 in which:

a. said arc chute has an exhaust passage at said exhaust end through which arcing products leave said are chute,

b. a housing is provided about said arc chute having wall portions spaced from said are chute to provide at said exhaust end of the arc chute and within said wall portions a chamber into which said arcing products can flow upon passing through said exhaust passage,

c. all of said chamber wall portions that are exposed to said arcing products while still ionized are electrically isolated from ground potential,

d. and said housing is sufficiently sealed to prevent the escape of still-ionized arcing products therefrom.

8. An electric circuit breaker as defined in claim 1 in which:

a. said are chute has an exhaust passage at said exhaust end through which arcing products leave said are chute,

b. a housing is provided about said arc chute having wall portions spaced from said are chute to provide at said exhaust end of the arc chute and within said wall portions a chamber into which said arcing products can flow upon passing through said exhaust passage,

c. all of said chamber wall portions that are exposed to said arcing products while still ionized are electrically isolated from ground potential,

d. the walls of said housing are substantially imperforate in the region of said exhaust passage to prevent arcing products from escaping from said housing through said walls in the region of said exhaust passage.

9. A circuit breaker as defined in claim 8 and further comprising structure at ground potential essentially contacting the outer surface of at least one of said chamber wall portions.

10. An electric circuit breaker as defined in claim 1 in combination with puffer means for developing a flow of gas into the region of said arc for driving said are along said runners during low current interruptions.

11. The circuit breaker of claim 1 in which said arc chute comprises spaced-apart plates of insulating material extending transversely of said are across the arcs path of travel for impeding motion of said are toward said exhaust end. I

12. The circuit breaker of claim 1 in which the interface between said ferromagnetic material and said refractory metal coating is free of brazing material.

13. The circuit breaker of claim 1 in which said refractory metal coating has a thickness less than 25 mils throughout most of the arc-exposed length of each runner.

14. The circuit breaker of claim 2 in which said refractory metal coating has a thickness less than 25 mils throughout most of the arc-exposed length of each run ner.

l I t t t 

1. An electric circuit breaker comprising an arc chute into which an arc is adapted to be driven for the purpose of extinguishing the arc, said arc chute having an exhaust end and comprising: a. a pair of spaced sidewalls of insulating material extending along the length of said arc as the arc moves within said chute, b. a pair of conductive arc runners spaced apart within said chute for defining paths along which the terminals of said arc travel as the arc moves within the arc chute, c. magnetic blow-out means for developing in the region between said runners a magnetic field that extends transversely of said paths for providing a force on said arc that moves said arc terminaLs along said runners towards said exhaust end, said magnetic blowout means comprising pole pieces located on the outer sides of said sidewalls in positions where at least one of said arc runners is located between said pole pieces, and coil means coupled to said pole pieces for developing said magnetic field when energized, d. each of said arc runners comprising elongated structure of ferromagnetic material and a coating of thermally-sprayed refractory metal bonded to a surface of said ferromagnetic structure for defining at the exposed side of the coating an arc-running surface along which one of said arc terminals moves, e. said thermally-sprayed coating comprising superimposed flattened and interlocking particles of refractory metal bonded together.
 2. The circuit breaker of claim 1 in which said refractory metal is arc-plasma sprayed tungsten.
 3. The circuit breaker of claim 1 in which said thermally-sprayed refractory metal coating covers substantially the entire surface of each of said arc runners that is exposed to an arc terminal.
 4. The circuit breaker of claim 2 in which said thermally-sprayed refractory metal coating covers substantially the entire surface of each of said arc runners that is exposed to an arc terminal.
 5. A circuit breaker as defined in claim 1 and further comprising: a. an arc-initiation region in which said arc is initiated, b. a probe projecting from one of said runners towards said arc-initiation region for accelerating arc transfer to said one runner, c. said probe having a body portion of ferromagnetic material joined to said one runner, d. and a coating of thermally-sprayed refractory metal covering the region of said body portion that is exposed to said arc.
 6. The circuit breaker of claim 1 in which: each of said arc runners has inactive surfaces that are free from said thermally-sprayed refractory metal coating, said inactive surfaces being constituted by a non-ferrous rust-resistant coating on said ferromagnetic material, and sealing means is provided between said refractory metal coating and said inactive surfaces for preventing said arc terminals from contacting said inactive surfaces.
 7. An electric circuit breaker as defined in claim 1 in which: a. said arc chute has an exhaust passage at said exhaust end through which arcing products leave said arc chute, b. a housing is provided about said arc chute having wall portions spaced from said arc chute to provide at said exhaust end of the arc chute and within said wall portions a chamber into which said arcing products can flow upon passing through said exhaust passage, c. all of said chamber wall portions that are exposed to said arcing products while still ionized are electrically isolated from ground potential, d. and said housing is sufficiently sealed to prevent the escape of still-ionized arcing products therefrom.
 8. An electric circuit breaker as defined in claim 1 in which: a. said arc chute has an exhaust passage at said exhaust end through which arcing products leave said arc chute, b. a housing is provided about said arc chute having wall portions spaced from said arc chute to provide at said exhaust end of the arc chute and within said wall portions a chamber into which said arcing products can flow upon passing through said exhaust passage, c. all of said chamber wall portions that are exposed to said arcing products while still ionized are electrically isolated from ground potential, d. the walls of said housing are substantially imperforate in the region of said exhaust passage to prevent arcing products from escaping from said housing through said walls in the region of said exhaust passage.
 9. A circuit breaker as defined in claim 8 and further comprising structure at ground potential essentially contacting the outer surface of at least one of said chamber wall portions.
 10. An electric circuit breaker as defined in claim 1 in combination with puffer means for developing A flow of gas into the region of said arc for driving said arc along said runners during low current interruptions.
 11. The circuit breaker of claim 1 in which said arc chute comprises spaced-apart plates of insulating material extending transversely of said arc across the arc''s path of travel for impeding motion of said arc toward said exhaust end.
 12. The circuit breaker of claim 1 in which the interface between said ferromagnetic material and said refractory metal coating is free of brazing material.
 13. The circuit breaker of claim 1 in which said refractory metal coating has a thickness less than 25 mils throughout most of the arc-exposed length of each runner.
 14. The circuit breaker of claim 2 in which said refractory metal coating has a thickness less than 25 mils throughout most of the arc-exposed length of each runner. 